Welcome to Android Central! It sounds like an issue with the camera itself, or perhaps the software. Does a reboot do anything? If not, try booting into Safe Mode, which disables all 3rd party apps temporarily. On most Android devices, you can get into Safe Mode by pressing and holding Power until the Power options come up (this is while the phone is on), then pressing and holding Power Off until the Safe Mode prompt appears. Tap Ok, and the phone will reboot into Safe Mode. If the problem persists, then it's likely a hardware or firmware problem. You would have to contact ZTE, or bring the phone to a repair shop.